The heads-up display (HUD) is an auxiliary display currently widely used in aircrafts and cars that project vehicle status information such as vehicle speed, engine RPM (revolution per minute), engine water temperature, whether the doors are closed, mileage, and fuel consumption on the windshield for the driver.
With the progress in three-dimension display techniques, the augmented-reality HUD (AR-HUD) has been developed, which produces virtual images in the environment outside the windshield to form labels corresponding to the real roads via the virtual images such that the driver can see the information displayed by the HUD by looking directly ahead at the real roads. As a result, safety and convenience of the driver are increased. However, if the AR-HUD cannot rapidly and accurately control the depth of field of the display image thereof, then labeling cannot be effectively performed under the constantly changing traffic conditions while driving.